Use of modified, low-viscosity sulfur as heat transfer and heat storage fluid

ABSTRACT

The invention relates to the use of a low-viscosity sulfur as a cost-effective heat transfer and heat storage fluid, the viscosity thereof being greatly reduced by saturation with hydrogen sulfide. Alternatively, the reduction in viscosity is optionally obtained by adding sulfur chloride. The melting point can be reduced by adding phosphorous. The temperature range of the use is from 130° C. up to 700° C. The fluid is particularly suitable for solar thermal power plants.

Liquids for transferring heat energy are used in various fields ofindustry. In internal combustion engines, mixtures of water and ethyleneglycol convey the waste heat of combustion into the radiator. Similarmixtures convey the heat from solar roof collectors into heat stores. Inthe chemical industry, they convey the heat from electrically heated orfossil-heated heating systems to chemical reactors, or from these tocooling devices.

In accordance with the profile of requirements thereon, a multitude ofliquids are used. The liquids should be liquid at room temperature oreven lower temperatures and in particular have low viscosities. Forrelatively high use temperatures, water is no longer an option; itsvapor pressure would be too great. Therefore, hydrocarbons are used upto 250° C., which usually consist of aromatic and aliphatic molecularmoieties. In many cases, oligomeric siloxanes are also used.

A new challenge for heat carrier liquids is that of solar thermal powerplants, which generate electrical energy on a large scale. Such powerplants have been built with a cumulative installed power of about 400megawatts to date. The solar radiation is focused by means of parabolicmirror troughs into the focus line of the mirrors. A metal tube locatedthere is within a glass tube to prevent heat losses, the space betweenthe concentric tubes being evacuated. A heat carrier liquid flowsthrough the metal tube. According to the prior art, a mixture ofdiphenyl ether and diphenyl is used here.

The heat carrier is heated to a maximum of 400° C., and it is used tooperate a steam boiler in which water is evaporated. This steam drives aturbine and this in turn drives the generator, as in a conventionalpower plant. Thus, overall efficiencies around 20 to 23% are achieved,based on the energy content of the solar radiation.

Both components of the heat carrier boil at 256° C. under standardpressure. The melting point of diphenyl is 70° C., that of diphenylether 28° C. The mixing of the two substances lowers the melting pointto about 10° C. The mixture of the two components can be used up to amaximum of 400° C., decomposition occurs at higher temperatures. Thevapor pressure at this temperature is about 10 bar, a pressure which canstill be managed efficiently in industry.

In order to obtain higher efficiencies than 20 to 23%, higher steaminput temperatures are needed. The efficiency of a steam turbine riseswith the turbine input temperature. Modern fossil-fired power plantswork with steam input temperatures up to 650° C. and thus achieveefficiencies around 45%. It would be entirely technically possible toheat the heat carrier liquid in the focus line of the mirrors totemperatures around 650° C. and hence likewise to achieve such highefficiencies; however, this is prevented by the limited thermalstability of the heat carrier liquids. There are obviously no organicsubstances which are capable of withstanding temperatures above 400° C.for a prolonged period; at least, none are known to date. There havetherefore been attempts to switch to inorganic, more thermally stableliquids.

The possibility, known from nuclear technology, of using liquid sodiumas a heat carrier liquid has been the subject of intense examination.However, practical use was opposed by the fact that sodium is quiteexpensive, that it has to be produced by electrolysis of sodium chloridewith high energy expenditure, and that it reacts even with traces ofwater to evolve hydrogen, thus constituting a safety problem.

Another possibility would be that of using inorganic salt melts as theheat carrier liquid. Such salt melts are prior art in processes whichwork at high temperatures. With mixtures of potassium nitrate, potassiumnitrite and the corresponding sodium salts, working temperatures up to500° C. are attained. The fertilizer industry is capable of producinglarge amounts. However, salt melts are not used in solar thermal powerplants because of two considerable disadvantages: being nitrates andnitrites, they have strongly oxidizing action at elevated temperatureson the metallic materials, preferably steels, as a result of which theupper use temperature thereof is limited to the approximately 500degrees mentioned. Due to their crystalline melting point, the lowermostuse temperature thereof is about 160° C.

The addition of nitrites or nitrates of alkaline earth metals achieves afurther lowering in the melting point, but this is at the cost of anincrease in the melt viscosity at low temperatures. In addition to anincrease in the pump energy, however, this adversely affects the heattransfer.

There have likewise been studies of whether water is suitable as a heatcarrier under appropriately high pressure. However, this is opposed bythe extremely high vapor pressure of more than 300 bar, which would makethe thousands of kilometers of pipelines in a large thermal solar powerplant uneconomically expensive. Steam itself is unsuitable as a heatcarrier due to its comparatively low thermal conductivity and the lowheat capacity per unit volume compared to a liquid.

A further problem arises from the aim of also operating a solar thermalpower plant during the night. For this purpose, considerable amounts ofheat carrier liquid have to be stored in large thermally insulatedtanks. If the intention is to store the heat content for a power plantwith an electrical power around one gigawatt for thirteen to fourteenhours, this requires tank fillings of the order of magnitude of onehundred thousand cubic meters at 600° C. and an efficiency around 40%from the heat reservoir to the generator output. This means that theheat carrier must be very inexpensive, otherwise the capital cost ofsuch a power plant will be uneconomically high. It also means thatsufficient material of the heat carrier must be available, since supplyon a large scale will require hundreds of one gigawatt units.

Thus, the solution to the question of economic supply with solar energyultimately depends on a large scale on whether there is a heat carrierliquid which enables temperatures up to 650° C. in constant use, whichhas a minimum, economically manageable vapor pressure at thistemperature, preferably up to ten bar, which does not oxidatively attackthe ferrous materials used and which has a minimum melting point.

At first glance, these conditions are most likely to be met by elementalsulfur. Sulfur is available in sufficiently large amounts. There arevery large, plentiful deposits of sulfur, and sulfur is obtained aswaste in the desulfurization of fuels and natural gas. At present, thereis no possible use for millions of tonnes of sulfur; it is stored in theform of large cast blocks or used to fill lake-sized soil formations.

The melting point of sulfur, at merely 120° C., is advantageously lowerthan the eutectic melting points of the currently used nitrate/nitritemixtures. The melting point of sulfur, at 444° C., is within the correctrange; decomposition is impossible. The vapor pressures are 2.1 bar at500° C., 3.9 bar at 550° C., and 6.6 bar at 600° C. The vapor pressureat 650° C. is around 10 bar, a pressure which is still easily manageableby technical means. Above 650° C., the equilibrium vapor pressure ofsulfur rises relatively steeply; at 700° C. it is 16.7 bar. Overall, thesulfur equilibrium vapor pressure is represented quite well by theequation log P (bar)=4.57579−3288.5/T (° K) (Thermodynamic Properties ofSulfur, James R. West, Ind. Eng. Chem., vol. 42, No. 4, 713 (1950)).

The density of liquid sulfur averages 1.6 kg/liter over wide temperatureranges, and the specific heat is around 1000 joules per kg and degree oraround 1600 joules per liter and degree. It is thus below that of waterat around 4000 joules per liter and degree, but above the specific heatof most customary organic heat carriers (substance data: Hans GüntherHirschberg, Handbuch Verfahrenstechnik and Anlagenbau [Handbook ofprocess engineering and plant construction], page 166, Springer Verlag1999, ISBN 3540606238).

However, elemental sulfur has a serious disadvantage for use as a heatcarrier liquid: within the temperature range from about 160 to 230° C.,the cyclic sulfur molecules polymerize with ring opening to give verylong chains. While the viscosity above the melting range is around 7mPas, it rises at 160° C. to 23 mPas, and attains maximum values around100 000 mPas at temperatures in the range from 170 to 200° C. Thepolymerization of sulfur to give chain molecules thus causes an enormousrise in viscosity, which means that the sulfur is no longer pumpablewithin this temperature range, and is thus unsuitable for application.

It was the aim of the invention to find a heat carrier liquid based onsulfur, which does not exhibit the disadvantage outlined above, the highviscosity rise.

It is known from the scientific literature that small additions ofhydrogen sulfide or halogens prevent the disadvantageous viscosity riseof sulfur. However, this finding has not been utilized to date in orderto employ sulfur as a heat carrier and storage liquid.

Heat carrier and heat storage liquids according to the invention thuscomprise, in addition to sulfur:

-   -   a) hydrogen sulfide in such an amount that it forms, within the        temperature range from 120 to 650° C., an equilibrium vapor        pressure of 0.1 to 10 bar, preferably of 1 to 3 bar,    -   b) optionally up to 10% by weight of a halogen, preferably        chlorine,    -   c) optionally up to 15% by weight of phosphorus.

Hydrogen sulfide causes the formation of shortened, low-viscosity sulfurchains with SH end groups or sulfane end groups. The chain lengthresults from the concentration of terminators used (Topics in CurrentChemistry, vol. 230, “Elemental Sulfur and Sulfur-Rich Compounds”,Springer, Heidelberg 2003, pages 92, 93).

Introduction of hydrogen sulfide into an unmodified sulfur melt over aperiod of 90 minutes and increasing the temperature from 125° C. to 190°C. completely prevented the rise in viscosity of the melt; 0.09 Pas wasmeasured instead of 93 Pas. The proportion by weight of hydrogen sulfidewhich dissolves in the sulfur melt is 0.01 to 1%.

A comparatively small viscosity increase occurs within the temperaturerange from 250 to 350° C., but this is much less than for unmodifiedsulfur. The melting point is lowered only slightly to temperaturesbetween 113 and 115° C.

Up to 370° C., the solubility of hydrogen sulfide in the sulfur meltincreases owing to the formation of the SH-terminated polysulfanes.Between 300 and 370° C., approx. 0.2% by weight of hydrogen sulfide isabsorbed at standard pressure (Wiewiorowski and Touro, J. Phys. Chem.,70, 234 (1966); R. Fanelli, “Solubility of Hydrogen Sulfide in Sulfur”,Ind. Eng. Chem. 41, 2031 -2033; Denis Yu Zezin et al. “The solubility ofgold in hydrogen sulfide gas: An experimental study”, Geochemica etCosmochimica Acta 71 (2007) 3070 - 3081).

This involves introducing the hydrogen sulfide into a stirred melt understandard pressure or elevated pressure within the temperature range from150° C. to 370° C. over a period of 1 to 5 hours. The reaction of thehydrogen sulfide with the sulfur chains is apparently slow due to thelow solubility, which requires the comparatively long reaction timesunder the customary laboratory conditions.

According to the invention, the hydrogen sulfide vapor pressure over thesulfur melt at 130° C. is 0.1 to 10 bar, preferably 1 to 3 bar. In theevent of a temperature increase, this pressure rises only slightly oreven falls because more hydrogen sulfide is converted to sulfane endgroups at rising temperatures.

The inventive liquid is produced by introducing hydrogen sulfide into asulfur melt within the temperature range from 250 to 350° C. untilsaturation, the ultimate vapor pressure of the hydrogen sulfide being0.1 to 10 bar, preferably 1 to 3 bar. In industrial performance, theapparatuses known in chemical process technology can be used for thispurpose, such as sparging stirrers or reaction mixing pumps, in whichthe melt is contacted with gaseous hydrogen sulfide under intensiveshear with high surface area, in order to keep the time until saturationof the sulfur melt to a minimum, much shorter than described in thescientific literature.

Both batchwise operations such as stirred tanks and, preferablycontinuous operations such as stirred tank cascades, flow tubes or thecombination of reaction mixing pumps with flow tubes or postreactionvessels can be used to produce the inventive liquids.

It is also possible to obtain the hydrogen sulfide by chemical reactionsdirectly in the sulfur melt. For example, it is only necessary to add0.01 to 2% by weight, preferably 0.1 to 0.5% by weight, of an alkalimetal hydrogensulfide to the sulfur melt, in the simplest case sodiumhydrogensulfide, which is commercially available in the form of flakeswith a water content around 30% by weight.

When the melt is heated to temperatures between 300 and 400° C.,hydrogen sulfide is released from the hydrogen-sulfides according to theoverall equation

2 MeHS—>Me₂S+H₂S.

The hydrogen sulfide thus formed reduces the length of sulfur chains asa result of sulfane formation.

The alkali metal sulfide formed reacts with the excess sulfur to give,in the case of sodium, sodium pentasulfide, which is insoluble in thesulfur melt according to the known phase diagrams (D. Lindberg, R.Backman, M. Hupa, P. Chartrand, “Thermodynamic evolution andoptimization of the Na-K-S system”, J. Chem. Therm. 38, p. 900-915(2006)).

Na₂S+S_(x)—>Na₂S₅

The alkali metal polysulfides formed are insoluble in the sulfur melt;above their melting point, they form droplets in the melt; below themelting point, for instance at 260° C. in the case of Na₂S₅, they formblack-brown flakes which are easy to remove from the sulfur melt byfiltration at low temperatures and viscosities, for example in thetemperature range from 130 to 200° C.

The hydrogen sulfide-containing sulfur melts produced by the differentvariants should be stored above their melting point in order to preventoutgassing of the hydrogen sulfide, caused by the crystallization ofsulfur. The sulfane end groups are apparently particularly stable in theliquid state. In the phase transition from liquid to solid, they woulddisrupt the crystal lattice; therefore, the system thus avoidseliminating hydrogen sulfide on crystallization.

At higher temperatures, just below the boiling point of the sulfur andwithout backpressure, i.e. also already at quite a high sulfur vaporpressure, hydrogen sulfide evaporates as expected, as a result of whichelevated viscosities are obtained again in the course of cooling. Inorder to avoid this, the heat carrier liquid should be used in a closedsystem of pipelines, pumps, control units and vessels. For reasons ofoperating reliability alone, all pipe connections, vessels and controlunits must be absolutely impervious; no hydrogen sulfide may escape.

It is also possible to lower the viscosity of the sulfur by the additionof halogens. The most active is chlorine which, introduced in the formof sulfur chlorides such as SCl₂ or S₂Cl₂, reacts to form SCl end groupsand thus lowers the chain length. When 0.75% chlorine is introduced intopure sulfur in the form of sulfur chlorides, the viscosity thereofwithin the temperature range from 150 to 320° C. is adjusted to valuesless than 0.2 Pas. The viscosity is thus lowered by a factor of 500(Topics in Current Chemistry, vol. 230, “Elemental Sulfur andSulfur-Rich Compounds”, Springer, Heidelberg 2003, pages 92, 93).

Halogens, preferably chlorine, are introduced as the end group byreaction of the sulfur melt with sulfur halides, preferably disulfurdichloride. Disulfur dichloride boils at 138° C. under standardpressure. It is mixed into the low-viscosity melt at 130° C. underambient pressure, then the temperature is increased under the vaporpressure which develops to 250° C. within one to two hours.

However, the use of hydrogen sulfide to lower the sulfur viscosity ispreferred because halogens at elevated temperatures can contribute tothe corrosion of the metallic materials used.

In some cases, the melting point of sulfur can be lowered by theaddition of phosphorus. The binary phase diagrams (Robert Fairman andBoris Ushkov, “Semiconducting Chalcogenide Glass”, Elsevier AcademicPress 2004, ISBN 01275 21879, 9780 1275 21879) show that a sulfur meltwhich contains 7 to 10% by weight (also approximately 7 to 10 atompercent) of phosphorus crystallizes at 80° C.

Phosphorus can be introduced into the sulfur melt as an element, butalso in the form of the sulfides, preferably as P₄S₁₀. In the sulfurmelt, the phosphorus is always present in pentavalent form owing to thesulfur excess.

In the studies for the invention, it was found that phosphorus hascrosslinking action on the sulfur melt and can thereforedisadvantageously increase the viscosity. Therefore, in the application,a decision will be made as to whether the lower melting point or thelower viscosity is more important for the end use.

In the presence of phosphorus sulfides, the risk of corrosion bychlorine is lower. On penetration of moisture into the heat carrier, thephosphorus sulfides are hydrolyzed more rapidly than the sulfur-chlorinebond, as a result of which the chloride-induced corrosion is suppressed.It is obvious that the inventive liquids must nevertheless be protectedfrom the ingress of moisture in production, storage, transport and use.

The variant of production of the hydrogen sulfide via the alkali metalhydrogensulfides cannot be used when the sulfur contains phosphorus. Inthis case, the melt reacts to form considerable amounts of solidsubstances, probably alkali metal salts of a thiophosphoric acid.

According to the Fairman reference, arsenic and silicon also lower thesulfur melting point. If the phase diagrams are examined experimentally,it is found that molar proportions of arsenic, introduced into the meltas arsenic trisulfide, increase the viscosity of the sulfur melt muchmore than phosphorus in equal molar proportions. For this reason andowing to its toxicity, arsenic is not an option as an additive forlowering the sulfur melting point. Silicon disulfide does not evendissolve in a sulfur melt under economically viable conditions, as aresult of which silicon is likewise not an option for lowering thesulfur melting point.

The operation of plants at temperatures up to 700° C. with the inventivelow-viscosity sulfur requires inexpensive materials which are stableagainst sulfidation at these temperatures. Specifically in recent times,steels have been developed for the power plant sector, which aresuitable for this use. Such ferrous materials have a ferritic structureand are free of nickel, the sulfides of which form low-melting phaseswith iron.

The most effective alloy constituent is aluminum, which forms animpervious, passivating oxide layer on the material surface. Such oldermaterials contain around 22% by weight of chromium and 6% by weight (11atomic %) of aluminum. They were known by the name ‘Kanthal’. For thepurpose of stabilization against sulfidation, it has been found that ahigh aluminum content is more important than a high chromium content.

With 8.5% by weight (16 atomic %) of aluminum, iron alloys are obtainedwith an expansion at room temperature by 20%, with 10% by weight (19atomic %) of aluminum expansions by 10%, and with 13 to 14% by weight(24 to 25 atomic %) of aluminum expansions by 3 to 5%.

With aluminum contents greater than 12% by weight (approx. 23 atomic %),sulfidation is completely suppressed at 800° C. under a particular mediacomposition (“Sulfidation/Oxidation Properties of Iron-Based AlloysContaining Niobium and Aluminum”, V. J. DeVan, H. S. Hsu, M. Howell, May1989, Oak Ridge National Laboratory, Fossil Energy Materials Program, AA15 10 10 0).

Improved iron alloys thus contain less chromium and more aluminum, asclaimed, for example, in EP 0652 297.

Described therein are alloys of composition 12 to 18 atomic % ofaluminum, 0.1 to 10 atomic % of chromium, 0.1 to 2 atomic % of niobium,0.2 to 2 atomic % of silicon, 0.01 to 2% by weight of titanium and 0.1to 5 atomic % of boron. Niobium, boron or titanium serve to causeseparation of fine grains of iron aluminide (Fe₃Al ) and to bind carbonin the form of carbides, which results in an improved toughness withexpansions above 3% and improved processability.

Iron alloys with even higher aluminum contents are more stable towardssulfur but are no longer processable under cold conditions. They areextruded or rolled at elevated temperatures. Such alloys, which areFe₃Al -base alloys, contain 21 atomic % of aluminum, 2 atomic % ofchromium and 0.5 atomic % of niobium, or 26 atomic % of aluminum, 4atomic % of titanium and 2 atomic % of vanadium, or 26 atomic % ofaluminum and 4 atomic % of niobium, or 28 atomic % of aluminum, 5 atomic% of chromium, 0.5 atomic % of niobium and 0.2 atomic % of carbon (EP0455 752).

Chromium-containing iron aluminide Fe₃Al with 3-5 atomic % of chromiummay have expansions of 20% at 100° C. (Oak Ridge National Laboratory).Alloys with 27 atomic % of aluminum, 9 to 10 atomic % of chromium and0.5 to 1 atomic % of niobium or molybdenum attain expansions by 20 to30% even at room temperature (EP 0455 752).

Molybdenum is a preferred alloy element because it counteracts thermaldecomposition of the dissolved hydrogen sulfide or of the sulfane endgroups to aluminum sulfide and hydrogen. Molybdenum catalyzes reactionof hydrogen with sulfur to give hydrogen sulfide.

The mechanical strength of iron alloys with a high aluminum content issufficiently great up to temperatures of 700° C. for use with theinventive heat carrier liquids.

However, it is also possible to treat oxidation-resistant materialsbased on iron with aluminum vapor or liquid aluminum, which forms, onthe surface, iron aluminides with high aluminum contents greater than 20atomic %, which have excellent protection against sulfidation. Suchcoatings are already used in the process industry and produced on acommercial basis.

With heat carrier liquids according to the invention, it is possible tooperate solar thermal power plants with efficiencies of fossil-firedpower plants, and to operate them day and night, without interruption,by means of storage tanks of appropriate dimensions for the hot liquid.Owing to the high efficiency, the capital costs per kilowatt hour fallby a factor of nearly 1.5 compared to the prior art.

It is also readily possible and advantageous to produce the inventiveliquids close to the site of use. Liquid sulfur is typically deliveredby ship. When, for example, 0.5% by weight of hydrogen sulfide is mixedcontinuously into 100 000 tonnes of sulfur, there are 500 tonnes ofhydrogen sulfide. The hydrogen sulfide need not be transported; it islikewise produced continuously on site. For this purpose, the chemicalindustry has developed elegant ambient-pressure processes by whichmolten sulfur and hydrogen can be used, under the action of catalysts,to produce just as much hydrogen sulfide as is required at that time(for example WO 2008/087086). In a subsequent stage, the hydrogensulfide is compressed to the pressure needed for mixing into the sulfurmelt. There is no need to store any great amount of hydrogen sulfide.

The hydrogen is likewise produced continuously as required on site, bythe electrolysis of water; the electrical power required for thatpurpose is drawn from adjacent power plants.

Owing to the favorable weight ratio of hydrogen to sulfur in thehydrogen sulfide, only about 30 tonnes of hydrogen are required for 500tonnes of hydrogen sulfide. Thus, for the production of 100 000 tonnesof the inventive liquid, by way of example, only about 30 tonnes ofhydrogen are needed. This corresponds to an energy expenditure of 10megawatts over the period of about 150 hours.

The possible disadvantage of the melting point around 116° C. without aphosphorus content to lower the melting point can be countered by designmeans with a low level of complexity by setting up the mirrors with aslight gradient and letting or sucking the heat carrier liquid out ofthe tubes just before sunset and storing it in the liquid state a fewdegrees above the melting point (for instance at 130° C.), inheat-insulated buffer tanks for operation the next day.

A particularly simple method is found to be the emptying of the part ofthe pipeline system to be cooled without a gradient in the construction,by forcing the sulfur out of the cooling pipelines briefly into thebuffer tank by means of the sulfur vapor pressure from thehigh-temperature section. Excess sulfur vapor condenses therein and inthe cooling pipeline sections.

This operation can be accomplished, for example, by temporarily openinga bypass to circumvent the pumps in the low-temperature section whichconvey the liquid against the vapor pressure and correspondingpressure-retaining valves. This does not give rise to any disadvantagefor the operation of a plant which works with the inventive heat carrierand heat storage liquid. It is not necessary to completely empty thepipeline system when care is taken in the course of construction of theplant that there are no moving parts, such as pumps or valves, in thecooling pipeline sections. In this case, residues of sulfur cancrystallize therein and be melted again without disadvantages.

Because the tanks for storage of the hot liquid must have anappropriately large volume and are additionally under the vapor pressureof the liquid, it is advantageous not to set up the tanks above ground,but to build them into the land surface. In this case, the liquid andvapor pressure can be absorbed by the masses of earth which surround thetank and the thermal insulation thereof.

However, the inventive heat carrier liquid is also suitable for allother fields of use of heat transfer and of heat storage in industry,which require an extremely wide temperature range of liquid phase andhigh temperatures.

Owing to its sulfur basis, it is the least expensive of allalternatives.

1. A method for transporting and storing thermal energy, said methodcomprising: providing a liquid that includes sulfur modified withinorganic components, and using said liquid for transport and storage ofthermal energy.
 2. The method of claim 1, wherein providing a liquidcomprises providing a liquid comprises comprising hydrogen sulfide,wherein the hydrogen sulfide vapor pressure of the liquid in the usetemperature range from 130 to 700° C. is 0.1 to 10 bar.
 3. The method ofclaim 2, wherein providing a liquid comprising hydrogen sulfidecomprises obtaining hydrogen sulfide by a chemical reaction in thepresence of the sulfur melt.
 4. The method of claim 1, wherein providinga liquid that includes sulfur modified by inorganic components comprisesproviding a liquid that includes up to 10 percent by weight of ahalogen.
 5. The method of claim 1, wherein providing a liquid thatincludes sulfur modified by inorganic components comprises providing aliquid having up to 15% by weight of phosphorus.
 6. The method of claim2, wherein the vapor pressure is between 1 bar and 3 bar.
 7. The methodof claim 4, further comprising selecting the halogen to be chlorine. 8.The method of claim 2, wherein providing a liquid that includes sulfurmodified by inorganic components comprises providing a liquid having upto 15% by weight of phosphorus.
 9. The method of claim 3, whereinproviding a liquid that includes sulfur modified by inorganic componentscomprises providing a liquid having up to 15% by weight of phosphorus.10. The method of claim 4, wherein providing a liquid that includessulfur modified by inorganic components comprises providing a liquidhaving up to 15% by weight of phosphorus.
 11. A composition of matterfor transporting or storing thermal energy, said composition comprisinga liquid that includes sulfur modified with inorganic components. 12.The composition of claim 11, wherein the liquid comprises hydrogensulfide, wherein the hydrogen sulfide vapor pressure of the liquid inthe use temperature range from 130 to 700° C. is 0.1 to 10 bar.
 13. Thecomposition of claim 11, wherein the sulfur is modified by up to 10percent by weight of a halogen.
 14. The composition of claim 13, whereinthe halogen is chlorine.
 15. The composition of claim 11, wherein theliquid includes up to 15% by weight of phosphorus.
 16. The compositionof claim 12, wherein the vapor pressure is between 1 and 3 bar.